Aggregatibacter actinomycetemcomitans (Aa) is intimately associated with Localized Aggressive Periodontitis (LAP) in young adults. Further, Aa possesses a variety of virulence traits that are consistent with pathogenic events that occur in LAP. Our group has been studying genes that are related to Aa-induced disease initiation and as such encode virulence traits responsible for Aa attachment, colonization, persistence, and subgingival survival. Thus far we have ascribed functions for two Aa autotransporter adhesin genes (aae and apiA) that are related to the specificity of Aa attachment to epithelium and have shown that these adhesins (as well as Leukotoxin) show species specificity for Old World (OW) primates and humans. This specificity makes the OW primate an ideal model for studying early events related to Aa infection with an eye toward development of preventive strategies. This R21 application consists of two Aims and is designed to compare oral colonization and persistence of two Aa strains (one from humans and one from Rhesus [Rh] monkeys) that are introduced into the oral cavity of OW primates. Each strain will be examined for its pattern, level of attachment, and colonization at different times over a 28-day period following introduction into the mouth of the monkey. Aim 1 will describe the topographical and quantitative level of Aa found in the mouths of Rh monkeys initially and then compare colonization and persistence of the two strains of Aa (one human and one monkey). Before placement, monkeys will receive scaling and prophylaxis plus chlorhexidine treatment. Animals will be fed Aa in a pancake and colonization and persistence will be analyzed 28 days after feeding. The Aa that colonizes and persists on teeth at a level equal to or greater than 1 x 102 /mL colonies of Aa will be selected for use in Aim 2. Aim 2 will assess the location, level and timing of Aa found on BECs, tongue and teeth comparing un-inoculated and wild type inoculated Aa to Aa with mutations in aae and apiA, a double knockout of aae/apiA, flp (the fibrillar outer protein) and ltx over a 28-day period. These experiments should reveal the importance of these genes in relation to Aa attachment to BECs (aae and apiA), to tooth colonization (flp) and to subgingival survival (ltx) in the oral cavity of OW primates. Establishing the utility of this model should allow us not only to dissect out attachment factors but also to unravel immune modulation factors from other Aa genes as they affect Aa pathogenesis in the future with an eye toward preventive strategies.